Coldest Temperature Ever Created

Image credit: NASA/JPL

Researchers from NASA and MIT have cooled sodium gas to the lowest temperature ever recorded – one-half billionth degree above absolute zero. At absolute zero temperature (-273 degrees Celsius), all molecular motion would stop completely since the cooling process has extracted all energy from the material. The gas needed to be confined in a magnetic field; otherwise it would stick to the walls of the container and be impossible to cool down. The researchers used a similar methodology that led to the Nobel Prize for Physics in 2001with the discovery of Bose-Einstein condesates (where the molecules move together in an orderly way at low temperatures).

NASA-funded researchers at the Massachusetts Institute of Technology (MIT), Cambridge, Mass., have cooled sodium gas to the lowest temperature ever recorded, one-half-billionth degree above absolute zero. This absolute temperature is the point, where no further cooling is possible.

This new temperature is six times lower than the previous record and marks the first time a gas was cooled below one nanokelvin (one billionth of a degree). At absolute zero (-273? Celsius or -460? Fahrenheit), all motion stops, except for tiny atomic vibrations, since the cooling process has extracted all energy from the particles.

By improving cooling methods, scientists have succeeded in getting closer to absolute zero. “To go below one nanokelvin is like running a mile below four minutes for the first time,” said Dr. Wolfgang Ketterle, a physics professor at MIT and co-leader of the research team.

“Ultra-low temperature gases could lead to vast improvements in precision measurements by allowing better atomic clocks and sensors for gravity and rotation,” said Dr. David E. Pritchard, MIT physics professor, pioneer in atom optics, atom interferometry, and co-leader of the team.

In 1995, a group at the University of Colorado, Boulder, Colo., and a MIT group led by Ketterle, cooled atomic gases to below one microkelvin (one millionth degree above absolute zero). In doing so, they discovered a new form of matter, the Bose-Einstein condensate, where the particles march in lockstep instead of flitting around independently. The discovery was recognized with the 2001 Nobel Prize in Physics, which Ketterle shared with his Boulder colleagues Drs. Eric Cornell and Carl Wieman.

Since the 1995 breakthrough, many groups have routinely reached nanokelvin temperatures; with three nanokelvin as the lowest temperature recorded. The new record set by the MIT group is 500 picokelvin or six times lower.

At such low temperatures, atoms cannot be kept in physical containers, because they would stick to the walls. Also, no known container can be cooled to such temperatures. To circumvent this problem, magnets surround the atoms, which keeps the gaseous cloud confined without touching it. To reach the record-low temperatures, the researchers invented a novel way of confining atoms, which they call a “gravito-magnetic trap.” The magnetic fields acted together with gravitational forces to keep the atoms trapped.

All the researchers are affiliated with the MIT physics department, the Research Laboratory of Electronics and the MIT-Harvard Center for Ultracold Atoms, funded by the National Science Foundation. Ketterle, Leanhardt and Pritchard co-authored the low-temperature paper, scheduled to appear in the September 12 issue of Science. NASA, National Science Foundation, the Office of Naval Research and the Army Research Office funded the research.

Ketterle conducts research under NASA’s Fundamental Physics in Physical Sciences Research Program, part of the agency’s Office of Biological and Physical Research, Washington. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology, Pasadena, manages the Fundamental Physics program.